Azeotropic distillation of methanol from admixture with acrylic esters



Patented Aug. 27, 1946 AZEOTROPIC DISTILLATION OF METHANOL FROM ADMIXTURE WITH ACRYLIC ESTERS Chessie E. Rehberg, Philadelphia, Pa., assignor to able boiling range.

United States of America as represented by Claude R. Wickard, Secretary of Agriculture,

and his successors in oiiice No Drawing.

Application December 27, 1943. Serial No. 515,799

2 Claims. 202-42) 1 This application is made under the act oi March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, it patented. may be manufactured and used by or for the Government of the United States of America to me of any royalty thereon.

alcoholysis.

In general, the hydrocarbons should boil at least 5 C., preferably even 15 C. or more, below the boiling point of the acrylic ester, but not below about 40 C.

Hexanes, mixtures of hexanes, and petroleum fractions are examples oi hydrocarbons which Also, they are This.

illustrated by the following 5 for governmental purposes without the payment y e u ed- The Optimum ca bon is one boiling as high as possible and yet distilling far This invention relates to amethod for removing enough below the ac ylic ester'to allow it to be alcohols from mixtures containing acrylic esters. readily p ed om t e y a fi The P The lower alkyl acrylates form azeotropic mixtieulal' boiling range selected with depend on the tures with several of the lower alkanols and distillation pm ntwhich is to e used. e hence these acrylates and alcohols cannot be sepemciency 0f the equipment, d e c mposition arated from each other by simple distillation. of the mixture being dihthled- It is often desirable, however, to be able to eflect liydmcflrbqns 0f the t d ri d do not form such a separation, as for example, in the preparaazeotlopes with acrylic esterstion of a higher acrylic ester from a lower one by 9 solvents the lower elkenols. 80 h Thus, in production of ethyl, when the alkanol-hydrocarbon azeotrope-is disbutyl decyly or other acrylic esters by the tilled and condensed the distillate separates into coholysis of methyl acrylate, methanol is formed an upper layer which is mostly hydrocarbon and and its continuous removal is desirable in order to lower layer which is mostly alkanolincrease the rate of reaction and the completeseparation is even marked when small ness of the conversion to the higher acrylate. amount of Water is'added to the distillate, The But Since methanol forms a binary azeotmpe with addition of 1 percent by volume of water is eilec-- methyl acrylate, the methanol cannot be distivetilled out of the reaction mixture without the The separation of the azeoh'opic distillate may simultaneous removal of methyl acrylate. A simhe n ntly carried out continuously during ilar difficulty is encountered in the alcoholysis of the distillation- For this purpose the distillate is ethyl acrylate, since ethanol and ethyl acrylat 0ndensed,.the hydrocarbon layer is continuously also form a binary azeotrope. Furthermore, in drawn ofi and returned to the stm while the l the production of ethyl, Drew] and isopmpyl cohol layer is continuously or, intermittently acryiates from methyl acrylate, numerous azeodrawn on from the sepammrtropes are encountered, among them being meth- My invention is anol binary azeotrones with methyl. ethyl. propyl examples: and isopropyl acrylates, ethanol binaries with EXAMPLE I methyl and ethyl acrylates, propanol binary with methyl acrylate and isopropanol binary with 2 111 188 (92 g.) of ethanol, 6 moles (5 8- methyl acrylate. Methanol also distills azeotropf methyl y ate, 's. of hydr quin 1 ically with methyl methacrylate. Accordingly, Sulfuric acid and 00 cciof a petroleum hyan object of this invention is to provide a method drocel'hon fraction having a boiling range of 58 for the separation of the lower alkanols, particu 40 Were refluxed in a k equ pped t larly methanol, from' admixture with acrylic e 3 fractichating co n. The column had a esters particularly methyl acrylate, total-condensation, partial take-oil head from I have found that the lower alk nol v n b which condensate could be either returned to the effectively separated from the lower acrylic esters column or sent into a contin us Separate! as azeotropes with aliphatic hydrocarbons of suit- Where pp or hydrocarbon layer, could be The hydrocarbons used continuously drawn Ofl and returned to the fracshould have a boiling point low enough to allow n ms column heel its pe column s separation from the acrylic ester by distillation I p r under total reflux until he t mper r but not so low as to decrease the reaction tem-' 5 0f the vapcrat the l-h dropped o out perature and rate of reaction unduly. "The lower 48 C. The rate of 'take-ofl was then adjusted boiling hydrocarbons should also be avoided beso that the methanol was removed inthe azeocause the percentage of alkanol in the azeotrope trope as rapidly as it was produced in the reaciormed is less as the boiling point decreases. tion. This was achieved by keeping the temperature of they vapor at the still-head at 45 to of removingthe methanol as its azeotrope with the hydrocarbon, it was removed as its azeotrope acid canbe made from methyl acrylate and the ,or butyl methacrylate and an appropriate alcohol, using a hydrocarbon liquid to remove am- [50 0., the take-oil being closed when the temperature exceeded 50 C. Methanol slowly collected in the lower layer of the condensate in the separator and was removed, either continuously or intermittently. This methanol layer contained a considerable amount of the hydrocarbon and it was found that much more complete separation could be achieved by adding a small amount of water either 'to the condensate in the separator or to the methanol layer after its withdrawal. e

After several hours of refluxing, the production of methanol ceased or became very slow,; the reaction having proceeded virtually to completion. The hydrocarbon was then distilledv out of the reaction mixture, leaving essentially a mixl ture of methyl and ethyl acrylatesl By frac-' .tional distillation of this mixture, an almost 1 quantitative yield of ethyl-acrylate was obtained.

EXAMPLE 11 Ethyl acrylate was prepared by proceeding as in Example I, except that the hydrocarbon was omitted from the reaction mixture, and instead with methyl acrylate (B. P. of azeotrope, 62 0.).

. 'I'he methanol-methyl acrylate azeotrope thus obtained contained about 50 to 55 percent of ;methanol which was removed by adding about one volume of the hydrocarbon (B. P. 58 to 61 C.) to three volumes of the azeotrope and distilling as i Example I. (In this way the "methanol-hydrocarbon azeotrope was distilled oil. the distillate was separated into two layers,

1 the hydrocarbon layer was returned to the still and the process continued until all methanol had been removed from the methyl acrylate.

A large number 01' higher esters of acrylic 4 finsteadof methyl acrylate and higher methacrylates can be made from methyl, ethyl, propyl 45 v 4 troplcally the lower alcohol as it is produced. Further; the lower aikanols can be removed from mixtures containing on or more lower alkyl acrylic esters irrespective of whether or not the mibiture arose from the alcoholysis of an acrylic es r.

Table Ishows the approximate boiling points of the alkanol azeotropes formed with a petroleum hydrocarbon fraction boiling substantially within the range 58 to 61 C. It should be understood that ,a hydrocarbon compound or mixture of compounds of other suitable boiling range might also be used and that the azeotrope formed by this material would have a different boiling point and different composition from that formed by the material boiling from 68 to 61 C.

TABLE I B. P. of azeotrope, C.

Alcohol Having thus described my invention, I claim: 1. In the process of preparing higher acrylic esters by the alcoholysis of methyl acrylate, the

step which comprises removing the methanol formed in the alcoholysis reaction by distilling it as an azeotrope with an aliphatic hydrocarbon having a boiling point at least 5 0. below the boiling point of methyl acrylate but not less than about C.

2. In the process of preparing higher acrylic esters by the alcoholysis oi methyl acrylate, the step which comprises removing the methanol formed in the alcoholysis reaction by distilling it as an azectrope with a petroleum fraction having a boiling point at least 5 C. below the boiling point of methyl acrylate but not less than about 40C.

. CHESSIE E. REHBERG. 

